That morning cup of coffee may be an antidote to post-exercise muscle soreness, if preliminary research is correct.

In a small study of female college students, researchers found that a caffeine supplement seemed to lessen the familiar muscle pain that crops up the day after a particularly challenging workout.

Known as delayed-onset muscle soreness, or DOMS, the pain is common in the day or two after a workout that was more intense than normal. Exercise that involves eccentric contraction of the muscles is particularly likely to cause delayed muscle pain.

In eccentric contraction, the muscle produces a force while it's being lengthened. This happens when a person runs downhill, for example, or lowers a weight during a bicep curl.

Exercisers and researchers alike have tried many ways to prevent DOMS -- including over-the-counter painkillers, stretching and massage -- but studies have found no cure-all for the problem.

In the current study, published in the Journal of Pain, researchers at the University of Georgia in Athens looked at the effects of a caffeine supplement on delayed muscle pain in nine young women.

First, in a simulated workout, the researchers used electrical stimulation to produce eccentric contractions in the women's thigh muscles -- enough to cause moderate day-after soreness.

Next, they repeated the procedure over the next two days, but on each day, the women took either a caffeine pill or placebo pill one hour before the muscle workout. Neither the women nor the researchers knew which pill was given on which day.

Overall, the women reported significantly less muscle soreness during the workout when they took caffeine instead of the placebo. The supplement had about the amount of caffeine found in two cups of coffee.

The theory is that caffeine eases delayed muscle pain by blocking the activity of a chemical called adenosine, which is released as part of the inflammatory response to injury. Adenosine can activate pain receptors in body cells, explained Victor Maridakis, the study's lead author.

In this study, he stated, the pain relief with caffeine was stronger than that from painkillers like acetaminophen (Tylenol) and naproxen (Aleve).

Maridakis noted that research into another popular pain reliever, ibuprofen, has shown inconsistent results, and it's unclear whether the drug -- sold under brand names like Advil and Motrin -- aids delayed muscle soreness.

Before downing a couple cups of joe before your workout, however, Maridakis recommends careful consideration of the possible side effects of caffeine.

"The negative side effects of caffeine are increased feelings of anxiety, heart palpitations, increased blood pressure, upset stomach, increased urination and disrupted sleep," he explained. "Caution should be used when consuming caffeine so not to exacerbate these side effects."

Though most people are "normal responders" to caffeine, Maridakis noted, some are hypersensitive to it and are at higher risk of side effects.

On the other end of the spectrum are the caffeine-resistant types. People who drink a couple cups of coffee a day tend to become desensitized to caffeine, the study authors point out, and it's unclear whether a dose of caffeine would aid their post-workout muscle pain.

SOURCE: Journal of Pain, February 2007.